signbitd.c

/* signbit() macro: Determine the sign bit of a floating-point number. Copyright (C) 2007 Free Software Foundation, Inc. This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>. */#include <config.h>/* Specification. */#include <math.h>#include <string.h>#include "isnan.h"#include "float+.h"#undef gl_signbitdint
gl_signbitd (double arg)
{
#if defined DBL_SIGNBIT_WORD && defined DBL_SIGNBIT_BIT/* The use of a union to extract the bits of the representation of a 'long double' is safe in practice, despite of the "aliasing rules" of C99, because the GCC docs say "Even with '-fstrict-aliasing', type-punning is allowed, provided the memory is accessed through the union type." and similarly for other compilers. */# define NWORDS \ ((sizeof (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))union { double value; unsignedint word[NWORDS]; } m;
m.value = arg;
return (m.word[DBL_SIGNBIT_WORD] >> DBL_SIGNBIT_BIT) & 1;
#elif HAVE_COPYSIGN_IN_LIBCreturn copysign (1.0, arg) < 0;
#else/* This does not do the right thing for NaN, but this is irrelevant for most use cases. */if (isnan (arg))
return 0;
if (arg < 0.0)
return 1;
elseif (arg == 0.0)
{
/* Distinguish 0.0 and -0.0. */staticdouble plus_zero = 0.0;
double arg_mem = arg;
return (memcmp (&plus_zero, &arg_mem, SIZEOF_DBL) != 0);
}
elsereturn 0;
#endif}